Project Summary/Abstract Triple-negative breast cancer (TNBC) accounts for 15-20% of breast cancer cases. The lack of targeted therapies and poor prognosis have resulted in a major effort to discover molecular targets to improve outcomes. While there is increasing understanding of the molecular heterogeneity of tumors, clinical trials of targeted agents have thus far been disappointing. Chemotherapeutic agents such as anthracycline and taxanes remain the backbone of medical management for both early and metastatic TNBC. This approach is toxic to normal in addition to tumor cells, leading to treatment burden and undesired side effects. These drugs are given to the patients in hope of the benefits to outweigh the risks. One significant approach to improve outcomes is the development of nanocarriers to achieve targeted delivery to tumors and reducing toxicity. To date, antitumor activities of the current FDA-approved nanomedicines (Doxil and Abraxane) have been moderate compared to the free drugs. There is an unmet need for an approach that can overcome different physiological barriers to deliver higher concentration of drugs in a more specific manner. Our long-term goal is to develop a platform to improve chemotherapeutics for achieving safer and more effective treatments. The objective is to develop a platform to overcome multiple barriers in tumor-specific delivery. We propose a biocompatible, non- immunogenic, self-assembling peptide-based nanofiber precursor (NFP). The factors that are essential in effective therapies are (a) co-delivering an optimal drug ratio of a combination therapy, (b) shape-controlled promotion of drug uptake, (c) charge-assisted tumor penetration, (d) enzyme-induced tumor retention (ETR), and (e) pH-activated controlled drug release approaches to be utilized by NFP. High PEG content of NFP minimizes its capture by the RES. Our overarching hypothesis is that such a multiplexed platform will significantly improve therapeutic efficacy and safety when used as a drug carrier. Our preliminary data have shown that NFP incorporated with doxorubicin has a superior therapeutic efficacy with minimal host toxicity compared to the free drug and Doxil. Our rationale is to maximize the delivery of NFP to the tumor, which requires us understand the contribution of NFP?s physicochemical properties (such as size and surface charges, ETR kinetics, and drug release profiles) in their biodistribution and uptake, penetration, and retention. Our specific aims will focus on the (Aim1) Refinement of different physicochemical properties, including size, shape, charge, and functional domains, affecting the in vivo behavior of NFP; and (Aim 2) Evaluation of the therapeutic efficacy of controlled- release NFP as a carrier of chemotherapy. This information will be critical for optimal formulation of multi-drug combinations in the most effective drug ratio to significantly improve the treatment outcomes. While we will utilize TNBC to develop the optimal characteristics of NFP, this information will be instrumental in designing drug combination involving NFP for other malignancies.